In recent years, an increasing incidence of adenocarcinomas and of more peripheral bronchial carcinomas has been observed, among other reasons due to changes in smoking habits (Stanley K. E., 1980, J. Natl. Cancer Inst, volume 65, pages 25-32). A highly promising radiotherapeutic approach lies in the introduction of stereotactic irradiation of the lungs. A disadvantage of this method, however, is the extensive technical outlay and time required (general anesthesia under high-frequency jet ventilation). Another approach lies in using navigated endoluminal irradiation by means of brachytherapy (Harms et al., 2001, Semin. Surg. Oncol., volume 20, pages 57-65). In the latter, a radioactive emitter is inserted through a catheter and placed directly in the tumor for a planned period of time. Because of the steep dose decline of the radiation source (Ir192), high-conformity dose distributions can be achieved which make it possible to protect surrounding normal tissue and to deliver high doses to tumors. Hitherto, brachytherapy could be used only for central forms of bronchial carcinoma. For this purpose, the irradiation catheter is introduced by a lung specialist with the aid of conventional bronchoscopy. Because of the extensive ramification of the bronchial tree and the associated problem of finding the correct path to more peripheral lung tumors, it has hitherto been possible to perform endoluminal irradiation only on tumors up to the 2nd level of segmental bronchi. This problem can be addressed by using an electromagnetic navigation system which, during the bronchoscopy, reveals the path to the more peripheral regions. Electromagnetic tracking systems with very small receiver coils that localize the catheter tip without direct viewing are already commercially available (e.g. AURORA, Northern Digital Inc., Waterloo, Ontario, Canada) and have already shown a high level of target accuracy. However, they have to be developed further in respect of their use in constantly moving soft-tissue parts, for example the lungs, and of the display of a pre-planned path to the target. Bronchoscopy navigation based on image data from computer tomography (CT) is known from the prior art (Superdimension, Herzliy, Israel, Schwarz et al., 2003, Respiration, volume 70, pages 516-522). However, the continuous ventilation of the lungs and the associated translocation of the bronchial tree make it much more difficult to determine the exact spatial relationship between the catheter tip and the bronchial tree. The approach of detecting the respiratory movement by means of markers applied to the chest and of taking this movement into account in position determination, leads to unsatisfactory results in the clinical application of this system. Particularly in the periphery of the bronchial tree, the system needs improving in terms of its precision, so that a combination of video image and virtual mapping sought by the physician is permitted. Here, it is not just the initial position of the irradiation catheter that is of interest, but also how its position is controlled throughout the treatment period.
In medical, diagnostic and therapeutic interventions on non-osseous, tubular organ structures, for example the blood vessels and bronchi of the human body, imaging methods have hitherto been used, for example high-intensity fluoroscopy, which always expose the patient and the treating physician to a radiation burden. Initial trials in navigation of tracked instruments, for example catheters or bronchoscopes, in non-osseous, tubular organ structures, are not adequate, in terms of their precision, for replacing these radiological imaging methods during the intervention.
In navigation in non-osseous, tubular organ structures, for example in navigated bronchoscopy, only external artificial or anatomical landmarks, or a small number of internal artificial or anatomical landmarks, have hitherto been used for recording a tracked instrument, for example a catheter or bronchoscope, using medical imaging data. Here, the skeleton of a tubular organ structure is not used for the recording in a catheter or bronchoscope.
Because of movements related to respiration within the thorax and abdomen, there is substantial organ displacement and deformation of the affected regions.
Registration points on the patient, or a small number of landmarks within the bronchus or a blood vessel, are not sufficient to ensure real-time recording of the tracked catheter or bronchoscope with previously recorded image data from computer tomography (CT) or magnetic resonance tomography (MRT). In bronchoscopy, for example, registration errors occur which make it difficult to perform reliable image-based tissue removal (biopsy) or intrabronchial irradiation and which increase the risk to the patient.